The present invention relates to a telescoping tube, and more particularly to a telescoping tube used automatically lift a door or similar device.
A telescoping tube can be filled with high pressure gas for lifting purposes, for example lifting a garage door or an automobile trunk lid, or other similar equipment requiring a lifting force. As shown in FIG. 1, a conventional telescoping tube used for lifting the trunk lid of a car is composed of a gas tube 10 with a piston rod 20. The gas tube 10 is filled with high pressure gas, such as nitrogen, and a lubricating oil. At one end of the gas tube 10 is provided a connecting piece 11 to be connected to the lid. A pair of sealing rings 12 and 13 are fixed in the tube 10 by engaging with annular projections 121 and 131 extending inwardly from the inner side of the tube 10, The annular projections 121, 131 are formed by a press process. A flexible gas-seal ring 14 is positioned between the fixed sealing rings 12 and 13. The piston rod 20 is connected to a piston 21 and extends outward from the closed end of the gas tube. A connecting piece 23 which is to be connected to the car body is attached to the outer end of the piston rod 20. When the user closes the trunk lid by applying a force F, the piston 21 is moved inward, dividing the gas tube 10 into two chambers. The piston 21 has a passage 22 to permit gas to flow therethrough during operation.
The above-mentioned prior art construction of the telescoping tube has two prominent shortcomings. First, the high pressure nitrogen gas within the gas tube 10 is liable to leak and a high precision process is needed to construct the fixed sealing ring 12, 13 and gas-seal ring 14 so as to achieve an effective gas-seal. In addition, after a period of use, the telescoping tube is liable to leak due to wear caused to the sealing ring. Second, once the gas leaks, the gas pressure will decrease and accordingly the lifting force will decrease.